Several US states now require light switches to provide dimmer functionality to meet energy efficiency requirements. Modern light switches provide a variety of means to control the dimmer functionality (e.g. rotational knobs, mechanical sliders and buttons operable to increase and decrease the light intensity). More recently solid state touch-sensitive electrical switches (e.g. dimmer switches) have been developed. Touch-sensitive switches eliminate the need for moving parts and instead can use capacitive touch technology and a touch-sensitive user interface surface. Without moving parts, touch-sensitive dimmer switches need a means to indicate operating point of the switch that does not rely on the position of a mechanical actuator. One method to achieve this is with a plurality of illuminated indicators (e.g. lights and LEDs) to indicate the operating point of the dimmer. Illuminated indicators are an effective visual indication of the dimmer set point, since they can be observed in dark conditions or from far away. However, using light to effectively convey the operating point of a dimmer switch is challenging. For example, LEDs are point light sources generated by small semiconductor junctions. It is therefore difficult to make large uniformly illuminated features with an LED. Hence indicator LEDs are typically a few millimeters in diameter. Materials in the dimmer switch (e.g. polymers) can also scatter light from LEDs, thereby causing indistinct indications.
Another challenge is to combine the illuminated indicators with the touch sensitive surface, thereby providing distinctly and uniformly illuminated regions of the touch sensitive surface. Previous attempts to illuminate the touch sensitive surface have used LEDs to directly illuminate small areas of the touch surface with point light sources. U.S. Pat. No. 4,246,494 issued to Foreman and U.S. Pat. No. 4,246,494 issued to Grinsphoon discloses touch sensitive dimmer switches but do not address the challenge of illuminating one or more segments of the touch sensitive portion of the switch. U.S. Pat. No. 5,336,979 issued to Watson discloses a touch based dimmer with a plurality of indicator lights (LEDs) to show the operating point of the dimmer switch. In the Watson disclosure, the indicator lights are located beside the touch sensitive surface and do not illuminate the touch sensitive surface. Additionally, Watson does not disclose any means to uniformly illuminate discrete segments of the touch-sensitive surface of the dimmer. The GRAFIK and Vierti dimmer switch product lines available from Lutron Inc. of Cooperstown Pa., use a plurality of LEDs behind a touch sensitive surface to indicate the dimmer operating point. The LEDs directly illuminate the user interface surface and the shape of the illuminated segments is determined primarily by the LED shape. The touch sensitive surface is narrow, and this is due in part to the spot size of the LEDs. The GRAFIK and Vierti products do not contain means to create uniformly illuminated distinct segments with well-defined edges. The GRAFIK and Vierti products do not provide means to tailor the shape of individual illuminated segments, so as to indicate the dimmer operating point. In a related challenge, previous illuminated dimmer switches do not provide means to uniformly illuminate a segment wider than a typical adult finger (e.g. wider than 1 centimeter).
Some light switch designs have used an LCD touch screen as the touch sensitive dimmer surface. These designs illuminate the entire backlight and use the liquid crystal layer to produce an indication of dimmer position. The liquid crystal layer has a dark appearance in the unenergized state and can diminish the aesthetic appeal of the dimmer switch. As far as I am aware no variable load control device (e.g. dimmer switch) previously disclosed, is effective to provide a touch sensitive surface with large, uniformly illuminated discrete segments.